The Liberal Democrats have been naive in government and have experienced a "particularly distressing" time since the general election, the party's president says.

In a message to party members attending the Lib Dem annual conference in Birmingham next week, Tim Farron says the party has suffered a loss of identity.

"Let's be realistic," Farron writes in the conference agenda. "The consequences of being in power and of not getting our messages across to the public at large have been particularly distressing.

"Clearly we have not succeeded in communicating our message, which has led to a loss of identity and … support. It may have been naive of us not to realise the threat we faced as the smaller party in a coalition government that does not have a single media outlet fighting our corner."

The criticism of failure to communicate is a reference to the row over tuition fees. There is a agreement in the party that, under pressure for abandoning its election pledge to vote against higher fees, Lib Dem minsters failed to explain the benefits of the new system – that graduates would not pay back loans until earning at least £21,000 a year.

The row over tuition fees was one of the factors that led to the Lib Dems' poor performance in the local elections in May. Farron addresses party members who may have lost seats when he says: "For many of you this is the first party conference of any sort since the recent elections. If you are coming to conference having lost your seat in May, I am particularly grateful and proud of you. You took the ultimate hit for our national decisions, and you did not deserve to lose."

But Farron says the party should not be despondent. "I am not prepared to simply accept that being in government means unpopularity, or that being in coalition means lost identity. If we want to go on changing the world and making a difference, losing elections is not a very smart way of going about it!

"But we absolutely cannot wallow in self pity; we must identify our threat, respect it and then show complete determination to overcome it."

Senior Lib Dems said they were relaxed with Farron's message which was approved by Nick Clegg's office. They said it was right to address the concerns of party members who lost council seats in May.

But they said the criticisms voiced by Farron applied to the party's performance before May. Lib Dem ministers have since been more assertive in government, notably over NHS reforms.

The health and social care bill passed its third reading in the commons on Thursday and will now be debated in the House of Lords. Any amendments in the upper house will have to be voted on by MPs.

Rebel Lib Dems, led by the former MP Evan Harris, will make a final push to table a motion at the conference calling for fresh amendments to the bill. If the motion, which was rejected in July, is turned down again they will seek to table an emergency motion in Birmingham.